This invention relates generally to porous materials. In particular, this invention relates to the preparation and use of porous films having a low dielectric constant.
As electronic devices become smaller, there is a continuing desire in the electronics industry to increase the circuit density in electronic components, e.g., integrated circuits, circuit boards, multichip modules, chip test devices, and the like without degrading electrical performance, e.g., crosstalk or capacitive coupling, and also to increase the speed of signal propagation in these components. One method of accomplishing these goals is to reduce the dielectric constant of the interlayer, or intermetal, insulating material used in the components. A method for reducing the dielectric constant of such interlayer, or intermetal, insulating material is to incorporate within the insulating film very small, uniformly dispersed pores or voids.
Porous dielectric matrix materials are well known in the art. One known process of making a porous dielectric involves co-polymerizing a thermally labile monomer with an dielectric monomer to form a block copolymer, followed by heating to decompose the thermally labile monomer unit. See, for example, U.S. Pat. No. 5,776,990. In this approach, the amount of the thermally labile monomer unit is limited to amounts less than about 30% by volume. If more than about 30% by volume of the thermally labile monomer is used, the resulting dielectric material has cylindrical or lamellar domains, instead of pores or voids, which lead to interconnected or collapsed structures upon removal, i.e., heating to degrade the thermally labile monomer unit. See, for example, Carter et. al., Polyimide Nanofoams from Phase-Separated Block Copolymers, Electrochemical Society Proceedings, volume 97-8, pages 32-43 (1997). Thus, the block copolymer approach provides only a limited reduction in the dielectric constant of the matrix material.
Another known process for preparing porous dielectric materials disperses thermally removable solid particles in a polymer precursor, polymerizing the polymer precursor without substantially removing the particles, followed by heating the polymer to substantially remove the particles. See, for example, U.S. Pat. No. 5,700,844. In the ""844 patent, uniform pore sizes of 0.5 to 20 microns are achieved. However, this methodology is unsuitable for such electronic devices as integrated circuits where feature sizes are expected to go below 0.25 microns.
Other methods of preparing porous dielectric materials are known, but suffer from broad distributions of pore sizes, too large pore size, such as greater than 20 microns, or technologies that are too expensive for commercial use, such as liquid extractions under supercritical conditions.
There is thus a need for improved porous dielectric matrix materials with substantially smaller pore sizes and a greater percent by volume of pores for use in electronic components, and in particular, as an interlayer, or intermetal, dielectric material for use in the fabrication of integrated circuits.
It has now been surprisingly found that certain polymers incorporated into a dielectric matrix provide, upon processing, porous films having a suitable dielectric constant and sufficiently small pore size for use as insulating material in integrated circuits. Such porogens provide dielectric matrix material having smaller pores, pores of lower degree of polydispersity, and, often, a greater percentage of pores by volume than known porogens.
In a first aspect, the present invention is directed to a method of preparing porous dielectric materials including the steps of: a) dispersing removable polymeric porogen in a B-staged dielectric material; b) curing the B-staged dielectric material to form a dielectric matrix material without substantially degrading the porogen; and c) subjecting the dielectric matrix material to conditions which at least partially remove the porogen to form a porous dielectric material without substantially degrading the dielectric material; wherein the porogen is substantially compatible with the B-staged dielectric material.
In a second aspect, the present invention is directed to porous dielectric matrix materials prepared by the method described above.
In a third aspect, the present invention is directed to a method of preparing an integrated circuit including the steps of: a) depositing on a substrate a layer of a composition including B-staged dielectric material having polymeric porogen dispersed therein; b) curing the B-staged dielectric material to form a dielectric matrix material without substantially removing the porogen; c) subjecting the dielectric matrix material to conditions which at least partially remove the porogen to form a porous dielectric material layer without substantially degrading the dielectric material; d) patterning the dielectric layer; e) depositing a metallic film onto the patterned dielectric layer; and f) planarizing the film to form an integrated circuit; wherein the porogen is substantially compatible with the B-staged dielectric material.
In a fourth aspect, the present invention is directed to an integrated circuit prepared by the method described above.
In a fifth aspect, the present invention is directed to a composition including a B-staged dielectric material and a polymeric porogen, wherein the porogen is substantially compatible with the B-staged dielectric material.